Process for testing a semiconductor device

ABSTRACT

A method for positioning a workpiece comprises the steps of providing a pedestal having a chamfered portion and a generally circular portion having a first diameter and providing a table having a hole therein and a chamfered portion, the hole having a second diameter larger than the first diameter. The inventive method further includes the steps of supporting the pedestal with the table, the chamfered portion of the table contacting the chamfered portion of the pedestal and placing the workpiece on the pedestal. Next, the chamfered portion of the pedestal is urged away from the table. Subsequent to the step of urging the chamfered portion of the pedestal away from the table, the pedestal is moved in at least one of X-, Y-, and theta directions while the generally circular portion of the pedestal extends into the hole in the table.

This is a division of application Ser. No. 08/636,449 filed Apr. 23,1996 and issued Jul. 15, 1997 as U.S. Pat. No. 5,648,728, which is acontinuation of application Ser. No. 08/205,678 filed Mar. 1, 1994,issued Apr. 23, 1996 as U.S. Pat. No. 5,510,723.

FIELD OF THE INVENTION

This invention relates to the field of semiconductor devicemanufacturing. More specifically, an apparatus for transporting andtesting an unpackaged semiconductor device is described.

BACKGROUND OF THE INVENTION

Many types of semiconductor devices are made using similar manufacturingprocedures. A starting substrate, usually a thin wafer of silicon, isdoped, masked, and etched through several process steps, the stepsdepending on the type of devices being manufactured. This process yieldsa number of semiconductor devices (dies) on each wafer produced. Eachdie on the wafer is given a brief test for functionality, and thenonfunctional devices are mechanically marked or mapped in software.This probe test is only a gross measure of functionality, and does notinsure that a device is completely functional or has specifications thatwould warrant its assembly in a package.

If the wafer has a yield of grossly functional devices which indicatesthat a significant number of devices from the wafer are likely to befully operative, the devices are separated with a die saw (diced) intodiscrete devices, and the nonfunctional devices are scrapped while thefunctioning devices are individually encapsulated in plastic packages ormounted in ceramic packages with one device in each package. After thediced devices are packaged they are rigorously electrically tested.Components which become nonfunctional or which operate below fullindustry specifications are scrapped or devoted to special uses.

Packaging unusable devices only to scrap them after testing is costly.Given the relatively low profit margins of commodity semiconductorcomponents such as dynamic random access memories (DRAMs) and staticrandom access memories (SRAMs), this practice is uneconomical. However,no thorough, cost effective, and automated method of testing anunpackaged device is available which would prevent this unnecessarypackaging of nonfunctional and marginally functional devices.

It is becoming more common to package multiple integrated circuitdevices as a single unit, known as a multi chip module (MCM). Testing ofeach device before it is assembled into the MCM is difficult because theconventional lead frame package is not typically used for themanufacture of MCMs. The reliability of the entire package iscompromised by the individual component with the least performancecapability. Although there is no industry standard by which devices aretested and considered "known good die," it is desirable to have theability to retest the individual die being used on a particular MCM toincrease the potential for greater yields. The ability to presort anindividual device is limited to results obtained through probe testing,which is only a gross measure of functionality and does not typicallyresult in information regarding access times or reliability. An MCM isburned in after assembly, which can result in the failure of one or moreDRAMs. If a single device is nonfunctional or operates outside ofacceptable specifications, the entire component fails and all devices inthe package are scrapped or an attempt is made to "re-work" the MCM.There is presently no cost-effective way to reclaim the functioningdevices.

Statistically, the yields of MCMs decrease in proportion to theincreasing number of devices in each module. The highest density moduleshave the lowest yields due to their increased total silicon surfacearea. Testing of unpackaged devices before packaging would be desirableas it would result in reduced material waste, increased profits, andincreased throughput. Using only known good devices in multichip moduleswould increase yields significantly. An apparatus which allows for thehandling and testing of an unpackaged semiconductor device would bedesirable. Similarly, an apparatus which would allow a user of diceddevices purchased from a manufacturer to test incoming devices would bedesirable.

SUMMARY OF THE INVENTION

An automated apparatus for testing an unencapsulated diced semiconductordevice comprises a test head. The test head comprises a carousel tablehaving a top and a bottom. A carousel table portion (which can be thecarousel table itself or an insert in the carousel table) has achamfered portion. The test head further comprises a chamfered pedestalreceived by the chamfered portion of the carousel table. The pedestalhas a bottom portion which extends through the carousel table below thecarousel table bottom. The semiconductor device to be tested is receivedby the pedestal.

The test head also has a chuck for receiving the bottom portion of thepedestal. The chuck is moveable in four directions, the X, Y, Z, andtheta directions. A probe is positioned above the pedestal for thepassage of an electric signal to the semiconductor device. The apparatusfurther comprises a camera for detecting a position of said proberelative to a position of the semiconductor device.

In operation, the chuck receives the bottom portion of the pedestal andurges the pedestal from the chamfered portion of the carousel tabletoward the probes. The chuck moves in the X, Y, and theta directionsresponsive to a signal from the camera to align the semiconductor devicewith the probes. The probes then make contact with the dicedsemiconductor device on the pedestal.

Objects and advantages will become apparent to those skilled in the artfrom the following detailed description read in conjunction with theappended claims and the drawings attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of one embodiment of the invention; and

FIG. 2 is a cross-section showing a test head assembly of FIG. 1.

It should be emphasized that the drawings herein are not to scale butare merely schematic representations and are not intended to portray thespecific parameters or the structural details of the invention, whichcan be determined by one of skill in the art by examination of theinformation herein.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a plan view of one embodiment of the invention. The flow of adiced device though the assembly as shown in FIG. 1 is generally fromleft to right.

Prior to testing the device with the inventive assembly, a semiconductorwafer 10 is produced according to means known in the art. The pluralityof devices 12 on the wafer 10 are diced, typically with a wafer saw, andremain attached to a carrier ring by an adhesive carrier film 16. Anumber of carrier rings 14 including wafers 16 are stored in a waferboat 18 for storage and for transportation to the test assembly.

An individual wafer carrier 14, or a boat 18 of wafers as shown in FIG.1, is placed in proximity to the inventive assembly. A single wafercarrier 14 is staged, for example on a module 20 which coarselypositions the wafer 10 in the X and Y directions. A module 20 such asthat produced by European Semiconductor Equipment Corporation (ESEC) ofPhoenix, AZ would function sufficiently, and other means for staging awafer of semiconductor devices would be possible and likely. A modulesuch as the ESEC module includes an assembly (not shown) for removingthe carrier from the boat and loading it onto the module platform. Thepositioning of the carrier on the module platform can be performed, forexample, with the aid of a camera (not shown), such as that availablefrom Cognex Corp. of Needham, Mass. The positioning of the camera andmovement of the module from information supplied by the camera can bedetermined by one of skill in the art from the information herein.

After the wafer carrier 14 is positioned on the module 20, each diceddevice 12 (or those found to be functioning during a probe test) isremoved from the carrier 14. With the ESEC module, removal pins (notshown) push up against the film 16 which attaches the device 12 to thecarrier 14 and pushes the back of the device and removes the device fromthe film. Simultaneously, a robot arm 22 picks up the device to betested 24, for example with a vacuum, and transports the device 24 tolocation one 26 on a test carousel 28. A robot such as a model 550 fromAdept Technology, Inc. of San Jose, Calif., a Model 6100 available fromCybeq of Menlo Park, Calif. or a number of other similar functioningserial communication articulated robotic arm (SCARA) or gantry typerobots, would function sufficiently. A mechanical precisor 30 as shown,which provides for theta alignment of the device 24, is an alternateembodiment which may have advantages. This may also be accomplished withtheta alignment by the robot arm. If a precisor is used, the precisor 30moves the device 24 to a known position on location one 26 of the testcarousel 28.

After the diced device is placed on location one of the test carousel,the carousel rotates to position the device at location two 32 which isthe test location. In FIG. 1 the carousel rotates 90° to position thedevice at the test head 34, although other possibilities are likely.

FIG. 2 is a cross section of the test head assembly 34 of location two32. The device test carousel 36 comprises a carousel table 38 having achamfered portion and a moveable chamfered test pedestal 40 with a hole42 for vacuum therethrough. The chamfered portion of the pedestal restson the chamfered portion of the carousel table. An alternate embodimentwhich has a hardened chamfered insert 44 in the carousel table 38 asshown for receiving the test pedestal 40 may improve themanufacturability of the carousel table 38. In any case, an X-Y-Z-thetatable 46 is positioned below the carousel table 38, and comprises achuck 48 having a port 50 for creating a vacuum and a base 52. In oneembodiment the base can be magnetic to facilitate coupling with the testpedestal 40. In the embodiment shown the chuck 48 and the pedestal 40have a space therebetween to allow for rotation of the carousel duringtransportation of the device. Other means for handling the chuck arepossible.

In operation, after the device 24 is moved from location one to locationtwo by rotation of the carousel 36 about an axis, the X-Y-Z-theta table46 moves in the Z direction (vertically) and the chuck 48 contacts thetest pedestal 40. The hole 42 in the pedestal 40 and the hole 50 in thechuck 48 mate, and a vacuum is imparted to a vacuum port 54 by meansknown in the art. The vacuum holds the device 24 into semirigid contactwith the pedestal 40. A depression or cavity on the pedestal can also beprovided to nest the device under test. An "O" ring 56 in the chuck 48reduces the loss of the vacuum to the device 24, although other meansfor reducing the vacuum loss are possible. Heated and cooled chucks,such as those available from Temptronics Corp. of Newton, Mass. may beused to test the device at temperatures other than ambient.

After the chuck 48 contacts the pedestal 40 and the vacuum is impartedto the device 24, the X-Y-Z-theta table 46 continues to rise, whichlifts the chamfered pedestal 40 from the chamfered portion 39 of thecarousel table 38 As the base of the pedestal is smaller than the holethrough the bottom of the hardened insert 44 (or through the table if aninsert is not used), the pedestal 40 is allowed some movement in the X-and Y- directions. A camera 56 (such as the Cognex as described above orsome other workable camera) positioned near a test mechanism 58 detectsthe position of a probe or probes 60 on the test mechanism 58 relativeto a position of the device 24 by movement of the X-Y-Z-theta table. Thecamera, therefore, can view both the die and the probes. By detectingthe position of the die, the position of contacts on the die (such asbond pads, not show) can be determined, or the contacts can be vieweddirectly and would provide equivalent results. A test mechanism 60 suchas a probe card or other means which allows for the passage of anelectrical signal between contacts on the device and the test mechanismwould function sufficiently. Probe cards which would function for thispurpose are available from several sources, such as Micro-Probe. Inc. ofSan Diego, Calif. As the X-Y-Z-theta table (and thus the device) israised, output from the camera allows a computer to coordinate movementof the X-Y-Z-theta table in the X-, Y-, and theta- directions to alignthe contacts on the device with the probes on the test mechanism. Amodel 1000 series available from Nutec Components of Deer Park, N.Y., orothers, can provide X-Y-theta alignment, and the Z-element can beprovided, for example, by Aerotec of Pittsburgh, Pa.

The device is raised in the Z-direction until the probes 60 makecontrolled contact with the bond pads (not shown) on the device 24. Aforce of three to five grams per bond pad would be sufficient to allowthe probe contacts 60 to make electrical connection with the bond pads.Additional forces can be applied as determined by the surface area ofthe contact and the geometry (i.e. spherical or flat) of the probe. Theforce can be measured by a GS-series pressure transducer available fromTransducer Techniques of Rancho California, Calif. or other workablemeans. Once the probes 60 on the test mechanism 58 contact the contacts(not shown) on the device 24, the circuitry on the device is tested bymeans known in the art, by connection of the probe card with a testersuch as a model Q2 tester from MegaTest Corporation of San Jose, Calif.After the device is tested the X-Y-Z-theta table is lowered so thepedestal 40 returns to the carousel table 38. The X-Y-Z-theta table isfurther lowered so the chuck 48 clears the pedestal 40, and the carousel36 is rotated to position the tested device 24 at location three of FIG.1.

The tested device 64 is moved by the robot 22 (or by a different similarrobot) to a sort carousel 66. The sort carousel receives the testeddevice. The placement of a tested device on the sort carousel can takeany number of configurations. For example, a diced device can be placedon one of four carrier rings 68 as shown in FIG. 1, with each carrierring being designated for devices having similar test performancecharacteristics (a total of four sort bins). It is further possible fora number of different arrays on each of the carrier rings to represent adifferent sort bin (16 bins shown in FIG. 1, with four sort bins on eachcarrier ring). Also, the carrier rings can be filled with tested devicesequentially with the test results being mapped in software for latersorting. Means for storage other than carrier rings, and theconfigurations other than those described, are possible and likely.

Once the carrier rings 68 (or other storage means) are filled withtested devices 64 as desired, they are moved from the sort carousel 66to a storage location, for example a boat 70, for later removal from thecarrier ring. A robot 72 such as a model ATM 100 series manufactured byEquipe Technologies of Mountain View, Calif. would function sufficientlyto move a carrier ring 68 from the sort carousel 66 to the storage boat70.

In another embodiment, a probe card can be used which does not have anaccess hole for viewing both the probes and the contacts on the die. Inthis embodiment, a prism is used to focus light reflected from the probeand contacts into the camera. The X-Y-Z-theta table moves responsive tosignals from the camera to align the contacts (such as bond pads) withthe probes on the probe card. Reference marks on the probe card and thepedestal may also be used to align the probe with the contacts on thedie.

While this invention has been described with reference to illustrativeembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the illustrative embodiments, as well asadditional embodiments of the invention, will be apparent to personsskilled in the art upon reference to this description. For example, itmay be possible to have more than one test head on the test carousel. Itis therefore contemplated that the appended claims will cover any suchmodifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. A process for transporting and testing anunpackaged semiconductor device comprising the following steps:staging asemiconductor wafer having a plurality of semiconductor devicesthereupon; moving one of said semiconductor devices onto a chamferedpedestal of a carousel table, said carousel table having a chamferedportion, said chamfered pedestal resting against said chamfered portionof said carousel table; positioning said semiconductor device at a testhead; lifting said pedestal from said carousel table toward a probe;responsive to a signal from a camera, moving said pedestal in at leastone of an X-, Y-, and theta direction to align said semiconductor devicewith said probe; contacting said probe and said semiconductor devicethereby making electrical contact between said semiconductor device andsaid probe; and testing said semiconductor device by passing anelectrical signal through said probe to said semiconductor device. 2.The process of claim 1 wherein said pedestal has a hole therethrough,said process further comprising imparting a vacuum through said hole insaid pedestal to said semiconductor device thereby holding saidsemiconductor device in semirigid contact with said pedestal.
 3. Theprocess of claim 1 further comprising the step of heating said pedestalto raise the temperature of said semiconductor device prior to saidtesting step.
 4. The process of claim 1 wherein said positioning stepcomprises rotating said carousel table about an axis.
 5. The process ofclaim 1 further comprising:rotating said carousel table subsequent tosaid testing step; removing said semiconductor device form saidpedestal; and placing said semiconductor device on an adhesive film of acarrier ring.
 6. The process of claim 5 further comprising the step ofplacing said semiconductor device on said adhesive film in accordancewith performance characteristics determined during said testing step. 7.A process used during the manufacture of a semiconductor devicecomprising the following steps:providing a semiconductor device;providing a pedestal supported by a table wherein said pedestal rests onsaid table, said table including a hole therein and an insert receivedby said hole; resting said pedestal on said insert of said table;placing said semiconductor device such that said pedestal supports saidsemiconductor device; urging said pedestal away from said table; andmoving said pedestal relative to said table to position saidsemiconductor device.
 8. The process of claim 7 wherein the step ofmoving said pedestal includes extending a portion of the pedestal intosaid hole.
 9. The process of claim 8 wherein said table and saidpedestal each comprise a chamfered portion and said step of providingsaid pedestal includes contacting said chamfered portion of said tablewith said chamfered portion of said pedestal as said pedestal rests onsaid table.
 10. The process of claim 8 wherein said step of moving saidpedestal further comprises moving said pedestal in at least one of X-,Y-, and theta directions.
 11. The process of claim 7 further comprisingthe step of contacting said semiconductor device with a test apparatusduring said step of urging said pedestal away from said table.
 12. Theprocess of claim 7 wherein said pedestal and said insert furthercomprise chamfered portions wherein said step of providing said pedestalincludes contacting said chamfered portion of said pedestal with saidchamfered portion of said insert.
 13. The process of claim 7 whereinsaid step of providing said semiconductor device includes providing anunpackaged semiconductor wafer section.
 14. The process of claim 7wherein said step of moving said pedestal is performed responsive todata from an optical input device, said step furthercomprising;contacting said semiconductor device with a test apparatus:and and testing said semiconductor device.
 15. A method for positioninga workpiece comprising the following steps:providing a pedestal having achamfered portion and a generally circular portion having a firstdiameter; providing a table having a hole therein and a chamferedportion, said hole having a second diameter larger than said firstdiameter; supporting said pedestal with said table, said chamferedportion of said table contacting said chamfered portion of saidpedestal; placing said workpiece on said pedestal; urging said chamferedportion of said pedestal away from said table; and subsequent to saidstep of urging said chamfered portion of said pedestal away from saidtable, moving said pedestal in at least one of X-, Y-, and thetadirections while said generally circular portion of said pedestalextends into said hole in said table.
 16. The process of claim 15further comprising the step of contacting said pedestal with a basewhich urges said chamfered portion of said pedestal away from saidtable.
 17. The process of claim 15 further comprising the step ofrotating said table subsequent to said step of placing said workpiece onsaid pedestal and prior to said step of urging said chamfered portion ofsaid pedestal away from said table.
 18. The process of claim 17 whereinsaid step of providing said table includes providing a table comprisingat least four holes therein wherein each said hole receives a differentchamfered pedestal therein.